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| Home > Publications database > Entwicklung von Schutzschichten für nicht-oxidische Faserverbundwerkstoffe |
| Book/Dissertation / PhD Thesis | FZJ-2021-00967 |
2021
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-524-6
Please use a persistent id in citations: http://hdl.handle.net/2128/27210
Abstract: The non-oxide ceramic matrix composites (CMCs), which exhibit good mechanical high-temperature properties and low density, represent a promising alternative to the temperature-limited metallic materials. However, a problem with these CMCs is their high susceptibility to corrosion in an atmosphere containing water vapor at temperatures above 1200°C. In order to protect the material from the influence of corrosive media, various protective coating systems (environmental barrier coatings, EBCs) are applied to the CMC. The aim of the work described here is to develop a coating system that protects the base material from corrosive atmospheres in cooperation with an industrial partner. The focus of the present work is on the manufacture and optimization of EBCs for the protection of silicon carbide-based CMCs. In a first step, different material candidates have been investigated for their thermal, thermomechanical, and mechanical properties to evaluate an optimal EBC candidate. In particular, the corrosion resistance against calcium-magnesium-aluminum-silicates (CMAS) has been considered. Subsequently, the best evaluated materials Yb$_{2}$Si$_{2}$O$_{7}$ and a mixture of Yb$_{2}$Si$_{2}$O$_{7}$ and Yb$_{2}$SiO$_{5}$ were applied to the CMC using different thermal spray processes. These two materials show a high corrosion protection against CMAS and coefficients of thermal expansion adapted to the CMC. Below the top layers of these two materials, the CMC is additionally coated with a silicon bond coat to create a complete EBC layer system. By varying the process parameters, it was possible to design the top layers in such a way that they were very dense, crackfree and crystalline at the same time. The layers developed with the different processes were subjected to evaluate the thermal shock resistance during thermal cycling and compared to each other. In addition to the material study and the optimization of layer deposition, the surface of the bond coat was structured with a laser to increase the adhesion of the top layer to the bond coat. In this way, the lifetime of the coatings was further increased. The effect of this structuring has been verified by means of an adapted test of interfacial toughness. It turned out that the interfacial toughness could be increased by 70% by means of the added structure. However, it was also found that the test methodology needs to be optimized, since the observed crack did not continuously follow the interface to be tested. In a final test series, the deposition of a Silicon-Yb$_{2}$Si$_{2}$O$_{7}$ layer system was transferred from flat substrates to a 3D substrate in the form of a turbine blade edge.
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